Many conventional projector displays include a display that modulates an illuminating light beam. The illuminating light beam may be a white light provided by a light source, such as metal halide lamps, xenon lamps, or mercury lamps. On the other hand, the illuminating light beam may include three separate color light beams, which are red, green, and blue light beams. Each color light beam may be separately provided by a light emitting diode (“LED”), a laser diode, or other types of laser such as gas laser, solid state laser, etc. The display panel may be a digital micro-mirror device (“DMD”) or micro-electro-mechanical system (“MEMS”) such as in a digital light processing (“DLP”) display system. The display panel may also be a liquid crystal display (“LCD”) or liquid crystal on silicon (“LCOS”) display.
Lasers have some advantages over other light sources. For example, their lifespan is about 10,000 hours in contrast to an approximately 1,500 hours of lifespan of mercury lamps. The brightness of lasers can be as high as 10,000 lumens, or more. In contrast, an LED projector lamp may provide approximately 1,000 lumens. A home theater projector may require at least 1,000 lumens. Lasers may also provide a wider color gamut as compared with traditional light sources.
In addition, a laser light source is compact in size, which may be more suitable for a pico projector. A pico projector is a projector used in handheld devices such as mobile phones, personal digital assistants, digital cameras, etc, which have little space to accommodate an attached display screen. Thus, a displayed image is projected onto any nearby viewing surface such as a wall.
The coherent nature of laser light can cause undesired laser speckles. A coherent laser beam incident on a non-specular reflecting surface such as a display screen or a wall, may be scattered with random phase by the surface. The random phase is caused by the random microscopic profile of the surface. When an observer looks at the projected image on the display screen or wall, the scattered light with random phase will interfere to form a speckle pattern in the retina of the observer. A speckle pattern is characterized by some spots appearing blacked out in a supposedly bright area. The blacked out spots appear to sparkle when there is relative movement between the scattering surface and the observer. Thus, the observer may perceive a projected image corrupted by a speckle pattern. Accordingly, a method or apparatus for reducing speckles is desirable.